How to update table while joining on CTE results in BigQuery?

Question

I think it will be obvious to see what I\'m trying to do through this simplified example (works in PostgreSQL)....

with a as
(
    select 1 as id, 123.456 as val         


        

Answer 1

You can transform you update statement into below

#standardSQL
UPDATE 
  `project.dataset.mytable` mytable 
  SET value = new_value 
FROM (
  WITH a AS
  (
    SELECT 1 AS id, 123.456 AS value
  )  
  SELECT a1.id a1_id, a2.id a2_id, 
    COALESCE(a1.value, a2.value) new_value
  FROM 
    a AS a1, 
    a AS a2 
)
WHERE 
  a1_id = mytable.id 
OR 
  a2_id = mytable.id2